Heterobranchia, the heterobranchs (meaning "different gill"), is a

taxonomic 280px, Generalized scheme of taxonomy Taxonomy is a practice and science concerned with classification or categorization. Typically, there are two parts to it: the development of an underlying scheme of classes (a taxonomy) and the allocation ...

clade In biology, a clade (), also known as a Monophyly, monophyletic group or natural group, is a group of organisms that is composed of a common ancestor and all of its descendants. Clades are the fundamental unit of cladistics, a modern approach t ...

snail A snail is a shelled gastropod. The name is most often applied to land snails, terrestrial molluscs, terrestrial pulmonate gastropod molluscs. However, the common name ''snail'' is also used for most of the members of the molluscan class Gas ...

s and

slug Slug, or land slug, is a common name for any apparently shell-less Terrestrial mollusc, terrestrial gastropod mollusc. The word ''slug'' is also often used as part of the common name of any gastropod mollusc that has no shell, a very reduced ...

s, which includes marine,

aquatic Aquatic means relating to water; living in or near water or taking place in water; does not include groundwater, as "aquatic" implies an environment where plants and animals live. Aquatic(s) may also refer to: * Aquatic animal, either vertebrate ...

, and

terrestrial Terrestrial refers to things related to land or the planet Earth, as opposed to extraterrestrial. Terrestrial may also refer to: * Terrestrial animal, an animal that lives on land opposed to living in water, or sometimes an animal that lives on o ...

gastropod Gastropods (), commonly known as slugs and snails, belong to a large Taxonomy (biology), taxonomic class of invertebrates within the phylum Mollusca called Gastropoda (). This class comprises snails and slugs from saltwater, freshwater, and fro ...

mollusc Mollusca is a phylum of protostome, protostomic invertebrate animals, whose members are known as molluscs or mollusks (). Around 76,000 extant taxon, extant species of molluscs are recognized, making it the second-largest animal phylum ...

s. Heterobranchia is one of the main clades of gastropods. Currently Heterobranchia comprises two groups: the opisthobranchs, and the

pulmonates Pulmonata or pulmonates is an informal group (previously an order, and before that, a subclass) of snails and slugs characterized by the ability to breathe air, by virtue of having a pallial lung instead of a gill, or gills. The group include ...

Diversity

The two subdivisions of this large clade are quite diverse: *

Opisthobranchia Opisthobranchs () is a now informal name for a large and diverse group of specialized complex gastropods which used to be united in the subclass Opisthobranchia. That taxon is no longer considered to represent a monophyletic grouping. Euopisth ...

are virtually all marine species, some shelled and some not, and comprise about 25 families and 2000 species of the bubble shells, the seaslugs, as well as the

sea hares The order Aplysiida, commonly known as sea hares (''Aplysia'' species and related genera), are medium-sized to very large opisthobranch gastropod molluscs with a soft internal shell made of protein. These are marine gastropod molluscs in the ...

. The internal organs of the opisthobranchs have undergone detorsion (unwinding of the viscera that were twisted during

torsion Torsion may refer to: Science * Torsion (mechanics), the twisting of an object due to an applied torque * Torsion of spacetime, the field used in Einstein–Cartan theory and ** Alternatives to general relativity * Torsion angle, in chemistry Bio ...

). * The

Pulmonata Pulmonata or pulmonates is an informal group (previously an order, and before that, a subclass) of snails and slugs characterized by the ability to breathe air, by virtue of having a pallial lung instead of a gill, or gills. The group includes ...

comprises about 20000 species, includes the majority of land snails and slugs, many freshwater snails, and a small number of marine species. The mantle cavity of the Pulmonata is modified into an air-breathing organ. They are also characterized by detorsion and a symmetrically-arranged nervous system. The pulmonates almost always lack an operculum and are

hermaphroditic A hermaphrodite () is a sexually reproducing organism that produces both male and female gametes. Animal species in which individuals are either male or female are gonochoric, which is the opposite of hermaphroditic. The individuals of many ...

Taxonomy

Current taxonomy

Heterobranchia *

Lower Heterobranchia Lower Heterobranchia, also known as the Allogastropoda, is a group of rather specialized, highly evolved sea slugs and sea snails, marine (ocean), marine gastropod mollusc, mollusks within the Subclass (biology), subclass Heterobranchia.WoRMS (20 ...

Valvatoidea Valvatoidea is a superfamily of minute freshwater and marine snails, aquatic gastropod mollusk Mollusca is a phylum of protostomic invertebrate animals, whose members are known as molluscs or mollusks (). Around 76,000 extant ...

Gray, 1840 **

Architectonicoidea Architectonicoidea is a superfamily of sea snails, marine gastropod mollusks in the informal group Lower Heterobranchia.Bouchet P. & Rocroi J.-P. (Ed.); Frýda J., Hausdorf B., Ponder W., Valdes A. & Warén A. 2005. ''Classification and nomencl ...

Gray, 1850 **

Mathildoidea Mathildoidea is a superfamily of sea snails, marine gastropod mollusks in the informal group Lower Heterobranchia.MolluscaBase eds. (2021). MolluscaBase. Mathildoidea Dall, 1889. Accessed through: World Register of Marine Species at: http://www ...

Dall, 1889 **

Omalogyroidea Omalogyroidea is a superfamily of minute sea snails, marine gastropod mollusks or micromollusks in the informal group Lower Heterobranchia Lower Heterobranchia, also known as the Allogastropoda, is a group of rather specialized, highly evolv ...

G. O. Sars, 1878 ** Allomorpha ***

Murchisonelloidea Murchisonelloidea is an unassigned superfamily of mostly very small sea snails, marine gastropod mollusks and micromollusks within the clade Heterobranchia.Gofas, S.; Rosenberg, G.; Bouchet, P. (2015). Murchisonelloidea Casey, 1904. Accessed th ...

Casey, 1904 *** Rhodopoidea Ihering, 1876 **

Orbitestelloidea Orbitestelloidea are a superfamily of minute sea snails, marine gastropod molluscs or micromolluscs in the infraclass Lower Heterobranchia.MolluscaBase eds. (2021). MolluscaBase. Orbitestelloidea Iredale, 1917. Accessed through: World Register ...

Iredale, 1917 ** Cimoidea Warén, 1993 *

Euthyneura Euthyneura is a taxonomic infraclass of snails and slugs, which includes species exclusively from marine, aquatic and terrestrial gastropod mollusks in the clade Heterobranchia. Euthyneura are characterised by several autapomorphies, bu ...

** Actenonacea ***

Acteonoidea Acteonoidea is a superfamily of sea snails, or bubble snails, marine gastropod mollusks. Taxonomy In the taxonomy of Bouchet & Rocroi (2005), the superfamily Acteonoidea has been included into the informal group "Lower Heterobranchia" (He ...

d'Orbigny, 1843 ***

Rissoelloidea Rissoellidae are a family of small sea snails, marine gastropod molluscs in the subclass Heterobranchia Heterobranchia, the heterobranchs (meaning "different gill"), is a taxonomic clade of snails and slugs, which includes marine, aquatic, ...

Gray, 1850 **

Tjaernoeiidae ''Tjaernoeia'' is a genus of sea snails, marine gastropod mollusks in the informal group Lower Heterobranchia. They are named after the marine laboratory at Tjärnö, Strömstad, Sweden. Their shells are rounded, thin and translucent. There are ...

Warén, 1991 **

Ringipleura Euthyneura is a taxonomic infraclass of snails and slugs, which includes species exclusively from marine, aquatic and terrestrial gastropod mollusks in the clade Heterobranchia. Euthyneura are characterised by several autapomorphies, but are n ...

*** Ringiculoidea Philippi, 1853 ***

Nudipleura Nudipleura are a clade of sea snails and sea slugs, marine gastropod mollusks within the large clade Heterobranchia. Taxonomy 2005 taxonomy In the taxonomy of Bouchet & Rocroi (2005), the clade Nudipleura is arranged as follows: *Clade N ...

Tectipleura Tectipleura is a subterclass of land and water-dwelling gastropods. The group consists of over 27,000 various species, among which are various groups of snails, slugs, and sea hares living across various diverse habitats around the world. It un ...

*** Euopistobranchia ***

Panpulmonata Panpulmonata is a taxonomic clade of snails and slugs in the clade Heterobranchia within the clade Euthyneura. Panpulmonata was established as a new taxon by Jörger et al. in October 2010. The older name "Pulmonata" referred to a group of euth ...

Older taxonomy

The families currently included in Heterobranchia have historically been placed in many different parts of the taxonomic class of gastropods. Earlier authors (such as J.E. Gray, 1840) considered Heterobranchia to consist of only marine gastropods, and conceptualized it as a borderline category, intermediate between the

, and all the other gastropods. The (sometimes recognized) category Heterostropha within the Heterobranchia, which includes such families as

Architectonicidae Architectonicidae, common name the staircase shells or sundials, are a family of sea snails, marine gastropod mollusks in the informal group Lower Heterobranchia (= Allogastropoda) of the clade Heterobranchia. The extinct families † Amphit ...

, the sundial or staircase snails, is primarily characterized by a shell which has a heterostrophic

protoconch A protoconch (meaning first or earliest or original shell) is an embryonic or larval shell which occurs in some classes of molluscs, e.g., the initial chamber of an ammonite or the larval shell of a gastropod. In older texts it is also called " ...

, in other words the apical whorls are coiled in the opposite plane to the adult whorls. The classification of this group was revised by Ponder & Warén in 1988. According to the older

taxonomy of the Gastropoda (Ponder & Lindberg, 1997) The Gastropoda#Taxonomy, taxonomy of the Gastropoda, as revised by Winston Ponder and David R. Lindberg in 1997, is an older Taxonomy (biology), taxonomy of the class Gastropoda, the Class (biology), class of molluscs consisting of all snails and s ...

the Heterobranchia were ranked as a superorder.

2005 taxonomy

Heterobranchia is currently one of the main clades of gastropods. For a detailed taxonomy, see Taxonomy of the Gastropoda (Bouchet & Rocroi, 2005)#Clade Heterobranchia.

2010 taxonomy

Jörger et al. (2010) have redefined major groups within the Heterobranchia: they created the new clades

Euopisthobranchia Euopisthobranchia is a taxonomic clade of snails and slugs in the clade Heterobranchia within the clade Euthyneura. This clade was established as a new taxon by Jörger et al. in October 2010. Euopisthobranchia is a monophyletic portion of the ...

and

. A

cladogram A cladogram (from Greek language, Greek ''clados'' "branch" and ''gramma'' "character") is a diagram used in cladistics to show relations among organisms. A cladogram is not, however, an Phylogenetic tree, evolutionary tree because it does not s ...

showing phylogenic relations of Heterobranchia as proposed by Jörger et al. (2010):